The invention generally relates to a method for calibrating a suspended seat system, and more particularly the invention relates to a method for automatically calibrating a suspended seat system by continuously updating maximum and minimum system endstop limits during use of the system.
Various methods have been employed to control vibration in seat suspension systems. Generally, in such prior art control methods operating conditions are obtained by at least one sensor which supplies system operating information to a processor that determines the appropriate primary control signal to be sent to an electro-mechanical device such as a magnetorheological (MR) fluid damper, for controlling vibration. A number of the various prior art methods for controlling vibration are described in the following issued United States patents: xe2x80x9cSkyhook Controlxe2x80x9d as described in U.S. Pat. No. 3,807,678 to Karnopp et al.; xe2x80x9cRelative Controlxe2x80x9d as described in U.S. Pat. No. 4,821,849 to Miller; xe2x80x9cObserver Controlxe2x80x9d as described in U.S. Pat. No. 4,881,172 to Miller; xe2x80x9cContinuously Variable Controlxe2x80x9d as described in U.S. Pat. No. 4,887,699 to Ivers et al.; xe2x80x9cDelayed Switching Controlxe2x80x9d as described in U.S. Pat. No. 4,936,425 to Boone et al.; xe2x80x9cDisplacement Controlxe2x80x9d as described in U.S. Pat. No. 5,276,623 to Wolfe; xe2x80x9cRate Controlxe2x80x9d as described in U.S. Pat. No. 5,652,704 to Catanzarite; xe2x80x9cModified Rate Controlxe2x80x9d as described in U.S. Pat. No. 5,712,783 to Method for AutoCalibration of a Controllable Damper Suspension System as described U.S. Pat. No. 5,964,455 to Catanzarite.
Seats used in large vehicles such as buses and trucks for example require suspension systems to limit the discomfort felt by the vehicle driver as a result of rough or uneven road conditions. Such suspension systems generally include an electro-mechanical device, such as a controllable orifice damper, magnetorheological damper or electrorheological damper, which is attached between two relatively moveable members. The device""s damping is controlled to minimize vibration, but also to avoid endstop collisions. For example, in a controllable damper suspension system, a variable damper is attached between two relatively moveable system components, such as a vehicle chassis and suspension or alternatively, between a vehicle seat and a structural body. One or more sensors provide information regarding the movement of the components of the system, for example, relative or absolute displacement, velocity or acceleration. The damping characteristics of the damper are then controlled in accordance with any of the aforementioned primary control methods. The control may also include an overriding end stop control method such as xe2x80x9cEndstop Control Methodxe2x80x9d described in U.S. Pat. No. 6,049,746 to Southward et al.
Under certain conditions, some or all of these primary control methods will result in abrupt collisions with the end stops (hereinafter referred to as xe2x80x9cend stop collisionsxe2x80x9d). An end stop collision occurs when the mechanical system in which the damper is connected hits the end stop, for example the maximum mechanical limits of the extension and/or rebound strokes when a sufficient transient load is encountered. If the system velocity is high enough when the end stop collision occurs, a very rapid impact can occur. The bottoming and topping out at an end stop condition imparts unwanted stresses to the mechanical components in the system and such collisions can be an annoyance to the driver. More significantly, when a driver or other seat occupant experiences endstop collisions, such collisions can effect the physical health of the seat occupant.
In order for controlled seat suspension systems to work properly the systems must be calibrated before they are installed for use in a particular application. Typically suspension system calibration is performed in the factory immediately after the seat is assembled. Current calibration methods are time consuming and complicated. In an effort to maintain high factory productivity, technicians do not always perform seat calibration and seats occasionally leave the factory without being calibrated yielding a poorly functioning system that is prone to end stop collisions.
One calibration method requires one or more electrical components to be electrically connected to the suspension system before executing the calibration procedure. The electrical component might be a shorting block or three-way jumper. The seat is then manually raised to the top of its travel to the top endstop and is lowered to the bottom of its travel to the bottom endstop. The endstop positions are stored in controller memory. Finally, the one or more electrical components are removed from the suspension system. Although not comprised of many steps, the foregoing prior art calibration method is time consuming and imparts a factory cost to the seat assembly process.
The calibration method disclosed in U.S. Pat. No. 5,964,455 cited hereinabove requires a means for raising and lowering the suspended seat during the calibration procedure in order to determine the upper and lower travel limits of the system. Execution of this calibration method is required for each seat because the seat suspension system is not functional until the system is calibrated. This prior art calibration system includes an auto-leveling device that controls airflow to the seat suspension and as a result the seat suspension height may be adjusted either manually by the driver or automatically by the calibration system. Using the auto-leveling device, the calibration routine is initiated by holding the auto-leveling switch in the up position. Once ready, the calibration routine raises the seat to the upper endstop, and stores the upper endstop position in controller memory. The seat is then moved to the lower endstop and the lower endstop is stored in controller memory. The seat is then moved to a calculated midheight position and is ready to be shipped to a customer. Although seat suspension systems were regularly calibrated using this method, the valving required to actuate the auto-leveling system greatly increased the cost of the suspension system.
The foregoing illustrates limitations known to exist in present devices and methods. Thus, it is apparent that it would be advantageous to provide an alternative calibration method directed to overcoming one or more of the limitations set forth above. Accordingly, a suitable alternative is provided including features more fully disclosed hereinafter.
In one aspect of the present invention, this is accomplished by providing an automatic calibration method for a seat suspension system. The method comprises the steps of sensing a current seat position; updating the value of a first current endstop to equal the current seat position if the seat position value is greater than a current first endstop limit; updating the value of a current second endstop limit to equal the current seat position if the sensed seat position is less than the current second endstop limit; determining if the current first endstop limit is greater than the stored first endstop limit; determining if the current second endstop limit is less than the stored second endstop limit; and if the current first endstop limit is greater than the stored first endstop limit, setting the stored first end stop limit equal to the current first endstop limit, and if the current second endstop limit is less than the stored second endstop limit setting the stored second endstop limit equal to the current second endstop limit.
The foregoing and other aspects will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawing figures.